“Refractive errors” are low-order aberrations, such as in an eye of a human. A “refractive prescription” is a prescription for corrective lenses (eyeglasses) that correct refractive errors. As described in more detail herein, eyes may also or instead suffer from higher-order aberrations.
Autorefractors automatically estimate a refractive prescription for a patient's eyes. While widely used in the United States and Europe for many years, autorefractors have a number of drawbacks. For example, autorefractors typically are quite expensive, often costing more than ten thousand dollars. In addition, autorefractors generally are large and immobile, and they require extensive assistance by an ophthalmologist, optometrist or her trained staff. Accordingly, for these and other related reasons, autorefractors are used much less frequently in low-resource settings, such as parts of Africa, Asia and even rural portions of the United States. Wavefront aberrometers are a complex and expensive type of autorefractor. Wavefront aberrometers are also used to guide laser surgery, such as for cataracts and vision correction.
Prescriptions may be expresses in optometric notation, power vectors notation and their equivalence.